Abstract
Abstract In the present study, the precipitation kinetics of topologically close-packed (TCP) Fe2Nb Laves and geometrically close-packed (GCP) Ni3Nb phases is studied quantitatively in experimental alloys with different Ta / Nb+Ta ratio, to clarify the mec4hanism of the Ta effect. The microstructure of alloys is changed from Widmanstätten structure to lamellar structure due to discontinuous precipitation, with increasing Ta / Nb+Ta. It is confirmed that Ta partitions into both Fe2Nb Laves and Ni3Nb phases. However, two phases stability is changed by added Ta content. Ta accelerates the formation kinetics of the precipitates at grain boundaries, as well as γ“-GCP phase within grain interiors, due to increased supersaturation by Ta addition. Besides, Ta retards the transformation kinetics of metastable γ“-Ni3Nb to stable the δ-Ni3Nb phase. The results indicate that Ta decreases the driving force for the transformation of the δ-GCP phase.
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